Ryu Kawamorita

Dosimetric comparison of RapidPlan and manually optimized plans in volumetric modulated arc therapy for prostate cancer

PURPOSE This study evaluated whether RapidPlan based plans (RP plans) created by a single optimization, are usable in volumetric modulated arc therapy (VMAT) for patients with prostate cancer. METHODS We used 51 previously administered VMAT plans to train a RP model. Thirty RP plans were created by a single optimization without planner intervention during optimization. Differences between RP plans and clinical manual optimization (CMO) plans created by an experienced planner for the same patients were analyzed (Wilcoxon tests) in terms of homogeneity index (HI), conformation number (CN), D95%, and D2% to planning target volume (PTV), mean dose, V50Gy, V70Gy, V75Gy, and V78Gy to rectum and bladder, monitor unit (MU), and multi-leaf collimator (MLC) sequence complexity. RESULTS RP and CMO values for PTV D95%, PTV D2%, HI, and CN were significantly similar (p<0.05 for all). RP mean dose, V50Gy, and V70Gy to rectum were superior or comparable to CMO values; RP V75Gy and V78Gy were higher than in CMO plans (p<0.05). RP bladder dose-volume parameter values (except V78Gy) were lower than in CMO plans (p<0.05). MU values were RP: 730±55MU and CMO: 580±37MU (p<0.05); and MLC sequence complexity scores were RP: 0.25±0.02 and CMO: 0.35±0.03 (p<0.05). CONCLUSIONS RP plans created by a single optimization were clinically acceptable in VMAT for patient with prostate cancer. Our simple model could reduce optimization time, independently of planners skill and knowledge.

Change in dose distribution of three-dimensional conformal radiotherapy during treatment for lung tumor.

PurposeWe investigated the changes in dose distribution of three-dimensional conformal radiotherapy (3D CRT) during lung tumor treatment.Materials and MethodsTen patients with non-small cell lung cancer who had undergone planning for radical radiotherapy were selected for study. Computed tomography (CT) examination was performed at two time intervals during the course of conformal radiotherapy: t0 Gy at the time of planning and t40 Gy at 40 Gy of treatment. We transferred all the planed beam data at t0 Gy to each t40 Gy CT image. The isodose distribution was recalculated at time t40 Gy for the same beam characteristics. Variations in volumes and dose-volume histograms (DVHs) were analyzed and compared for lung, gross target volume (GTV), and planning target volumes (PTV) between t0 Gy and t40 Gy. A paired t-test was performed to compare the DVH between t0 Gy and t40 Gy.ResultsThe mean minimum doses for t40 Gy GTV, and PTV were lower than t0 Gy. However, there was no significant difference between t0 Gy and t40 Gy (p=0.493, 0.378, respectively). There was a patient whose minimum doses of GTV and PTV were decreased and who had notable improvement of lobar atelectasis after 40 Gy of radiotherapy. Comparison of the percent volume of received dose exceeding 20 Gy (V20) and the mean dose for the total lung revealed that t40 Gy was larger than t0 Gy (p=0.013, 0.012).ConclusionIncorporation of the time factor into 3D treatment planning is mandatory for frequent reiteration of treatment planning during treatment periods. Clearly, more work in this area should be considered.

Comparison of dosimetric parameters and acute toxicity after whole-pelvic vs prostate-only volumetric-modulated arc therapy with daily image guidance for prostate cancer.

OBJECTIVE To compare dosimetric parameters and acute toxicity rates between whole-pelvic (WP) and prostate-only (PO) volumetric-modulated arc therapy (VMAT) in patients with localized prostate cancer. METHODS A total of 224 consecutive patients treated with definitive VMAT to 78 Gy in 39 fractions were enrolled. Of these, 119 patients received initial WP VMAT at 46.8 Gy in 26 fractions using a simultaneous integrated boost technique, and 105 patients received PO VMAT. Image-guided radiotherapy was practised with daily cone beam CT. RESULTS The mean rectal dose, the rectal volume receiving ≥30 Gy (V30Gy), rectal V50Gy, the mean bladder dose, bladder V30Gy and bladder V50Gy were significantly increased in the WP group (p < 0.05 each); however, the rectal V70Gy did not differ between groups (p = 0.101), and the bladder V70Gy was significantly lower in the WP group (p = 0.029). The WP group experienced a significantly increased frequency of acute grade 2 diarrhoea relative to the PO group (5.9% vs 0%; p = 0.015). No differences were seen between the WP and PO groups in terms of acute grade 2 proctitis (10.1% vs 6.7%; p = 0.360) and genitourinary (GU) toxicity (12.6% vs 10.5%; p = 0.620). CONCLUSION Despite larger rectum and bladder volumes at low- and medium-dose levels, WP VMAT resulted in no significant increase in acute proctitis or GU toxicity when compared with PO VMAT. ADVANCES IN KNOWLEDGE This study demonstrates that whole-pelvic radiotherapy has comparable acute toxicity to those observed with prostate-only radiotherapy when VMAT with daily image guidance is used.

Whole-pelvic volumetric-modulated arc therapy for high-risk prostate cancer: treatment planning and acute toxicity

The objectives of this study were to evaluate dosimetric quality and acute toxicity of volumetric-modulated arc therapy (VMAT) and daily image guidance in high-risk prostate cancer patients. A total of 100 consecutive high-risk prostate cancer patients treated with definitive VMAT with prophylactic whole-pelvic radiotherapy (WPRT) were enrolled. All patients were treated with a double-arc VMAT plan delivering 52 Gy to the prostate planning target volume (PTV), while simultaneously delivering 46.8 Gy to the pelvic nodal PTV in 26 fractions, followed by a single-arc VMAT plan delivering 26 Gy to the prostate PTV in 13 fractions. Image-guided RT was performed with daily cone-beam computed tomography. Dose–volume parameters for the PTV and the organs at risk (OARs), total number of monitor units (MUs) and treatment time were evaluated. Acute toxicity was assessed using the Common Terminology Criteria for Adverse Events, version 4.0. All dosimetric parameters met the present plan acceptance criteria. Mean MU and treatment time were 471 and 146 s for double-arc VMAT, respectively, and were 520 and 76 s for single-arc VMAT, respectively. No Grade 3 or higher acute toxicity was reported. Acute Grade 2 proctitis, diarrhea, and genitourinary toxicity occurred in 12 patients (12%), 6 patients (6%) and 13 patients (13%), respectively. The present study demonstrated that VMAT for WPRT in prostate cancer results in favorable PTV coverage and OAR sparing with short treatment time and an acceptable rate of acute toxicity. These findings support the use of VMAT for delivering WPRT to high-risk prostate cancer patients.

A dosimetric comparison of RapidArc and IMRT with hypofractionated simultaneous integrated boost to the prostate for treatment of prostate cancer

OBJECTIVE To compare the dosimetric results and treatment delivery efficiency among RapidArc® (Varian Medical Systems, Palo Alto, CA), 7-field intensity-modulated radiotherapy (7-f IMRT) and 9-field IMRT (9-f IMRT) with hypofractionated simultaneous integrated boost to the prostate. METHODS RapidArc, 7-f IMRT and 9-f IMRT plans were created for 21 consecutive patients treated for high-risk prostate cancer using the Eclipse™ treatment planning system (Varian Medical Systems). All plans were designed to deliver 70.0 Gy in 28 fractions to the prostate planning target volume (PTV) while simultaneously delivering 50.4 Gy in 28 fractions to the pelvic nodal PTV. Target coverage and sparing of organs at risk (OARs) were compared across techniques. The total number of monitor units (MUs) and the treatment time were used to assess treatment delivery efficiency. RESULTS RapidArc resulted in slightly superior conformity and homogeneity of prostate PTV, whereas all plans were comparable with respect to dose to the nodal PTV. Although OARs sparing for RapidArc and 7-f IMRT plans were almost equivalent, 9-f IMRT achieved better sparing of the rectum and bladder than RapidArc and 7-f IMRT. RapidArc provided the highest treatment delivery efficiency with the lowest MUs and shortest treatment time. CONCLUSION RapidArc resulted in similar OAR sparing to 7-f IMRT, whereas 9-f IMRT provided the best OAR sparing. Treatment delivery efficiency is significantly higher for RapidArc. ADVANCES IN KNOWLEDGE This study validated the feasibility and limitations of RapidArc in the treatment of high-risk prostate cancer with complex pelvic target volumes.

Optimal bladder volume at treatment planning for prostate cancer patients receiving volumetric modulated arc therapy

PURPOSE To investigate optimal bladder volumes at treatment planning (TP) in prostate cancer patients who undergo volumetric modulated arc therapy (VMAT). METHODS AND MATERIALS To determine the minimum value, 122 patients were classified into 6 groups according to the bladder volume at TP: <100 mL (group 1), 100-149 mL (group 2), 150-199 mL (group 3), 200-249 mL (group 4), 250-299 mL (group 5), and ≥300 mL (group 6). Bladder volumes receiving more than 70 Gy (V70Gy) and V50Gy were calculated in each subgroup and compared with the bladder dose-volume constraints specified in our institution. To determine the maximum value, 64 patients who underwent uniform nursing interventions were classified into the same 6 groups. Bladder volumes on cone beam computed tomography (CBCT) images were measured once weekly during treatment, for a total of 8 measurements. Relative bladder volumes (bladder volume on CBCT image [mL]/bladder volume at TP [mL] × 100%) were evaluated in each of the 6 subgroups. RESULTS The upper bounds of the 95% confidence intervals of the mean V70Gy and V50Gy values in group 1 exceeded the dose constraints at our institution. The mean relative bladder volumes were 104%, 91%, 77%, 81%, 63%, and 59% in groups 1, 2, 3, 4, 5, and 6, respectively. The institutional criterion of 70% for the mean relative bladder volume was achieved in groups 1-4, but it could not be achieved in groups 5-6. Therefore, the patients in groups 2-4 met both institutional dose constraints for the bladder at TP and the institutional criterion for the mean relative bladder volume during treatment. CONCLUSIONS The optimal bladder volumes at TP were between 100 and 250 mL in this setting. Nursing intervention needs to be implemented before treatment planning to ensure that patients achieve the optimal bladder volume range.

A treatment-planning comparison of three beam arrangement strategies for stereotactic body radiation therapy for centrally located lung tumors using volumetric-modulated arc therapy

The purpose of this study was to determine appropriate beam arrangement for volumetric-modulated arc therapy (VMAT)-based stereotactic body radiation therapy (SBRT) in the treatment of patients with centrally located lung tumors. Fifteen consecutive patients with centrally located lung tumors treated at our institution were enrolled. For each patient, three VMAT plans were generated using two coplanar partial arcs (CP VMAT), two non-coplanar partial arcs (NCP VMAT), and one coplanar full arc (Full VMAT). All plans were designed to deliver 70 Gy in 10 fractions. Target coverage and sparing of organs at risk (OARs) were compared across techniques. PTV coverage was almost identical for all approaches. The whole lung V10Gy was significantly lower with CP VMAT plans than with NCP VMAT plans, whereas no significant differences in the mean lung dose, V5Gy, V20Gy or V40Gy were observed. Full VMAT increased mean contralateral lung V5Gy by 12.57% and 9.15% when compared with NCP VMAT and CP VMAT, respectively. Although NCP VMAT plans best achieved the dose–volume constraints for mediastinal OARs, the absolute differences in dose were small when compared with CP VMAT. These results suggest that partial-arc VMAT may be preferable to minimize unnecessary exposure to the contralateral lung, and use of NCP VMAT should be considered when the dose–volume constraints are not achieved by CP VMAT.

Minimizing dose variation from the interplay effect in stereotactic radiation therapy using volumetric modulated arc therapy for lung cancer

Abstract It is important to improve the magnitude of dose variation that is caused by the interplay effect. The aim of this study was to investigate the impact of the number of breaths (NBs) to the dose variation for VMAT‐SBRT to lung cancer. Data on respiratory motion and multileaf collimator (MLC) sequence were collected from the cases of 30 patients who underwent radiotherapy with VMAT‐SBRT for lung cancer. The NBs in the total irradiation time with VMAT and the maximum craniocaudal amplitude of the target were calculated. The MLC sequence complexity was evaluated using the modulation complexity score for VMAT (MCSv). Static and dynamic measurements were performed using a cylindrical respiratory motion phantom and a micro ionization chamber. The 1 standard deviation which were obtained from 10 dynamic measurements for each patient were defined as dose variation caused by the interplay effect. The dose distributions were also verified with radiochromic film to detect undesired hot and cold dose spot. Dose measurements were also performed with different NBs in the same plan for 16 patients in 30 patients. The correlations between dose variations and parameters assessed for each treatment plan including NBs, MCSv, the MCSv/amplitude quotient (TMMCSv), and the MCSv/amplitude quotient × NBs product (IVS) were evaluated. Dose variation was decreased with increasing NBs, and NBs of >40 times maintained the dose variation within 3% in 15 cases. The correlation between dose variation and IVS which were considered NBs was shown stronger (R 2 = 0.43, P < 0.05) than TMMCSv (R 2 = 0.32, P < 0.05). The NBs is an important factor to reduce the dose variation. The patient who breathes >40 times during irradiation of two partial arcs VMAT (i.e., NBs = 16 breaths per minute) may be suitable for VMAT‐SBRT for lung cancer.

Bowel and urinary quality of life after whole-pelvic versus prostate-only volumetric-modulated arc therapy for localized prostate cancer

PURPOSE This study aimed to compare bowel and urinary health-related quality of life (HRQOL) between prostate-only (PO) volumetric modulated arc therapy (VMAT) and whole-pelvis (WP) VMAT in patients with localized prostate cancer. METHODS AND MATERIALS A total of 234 patients treated with definitive VMAT to 78 Gy in 39 fractions were enrolled. Of these, 108 patients received PO-VMAT and 126 patients received initial WP-VMAT to 46.8 Gy in 26 fractions using a simultaneous integrated boost technique. HRQOL was prospectively assessed before radiation therapy (baseline), and 3, 6, 12, and 24 months after treatment using the Expanded Prostate Cancer Index Composite (EPIC). RESULTS Baseline HRQOL scores did not differ significantly between the 2 groups. No significant between-group differences in HRQOL change from baseline were observed for all bowel and urinary EPIC domains. The proportion of patients showing a clinically relevant decrease in bowel and urinary HRQOL scores from baseline was similar between the groups throughout the follow-up period. An analysis of individual HRQOL items showed that patients undergoing WP-VMAT were more likely to report moderate/big problems with bloody stools (P = .039) and overall bowel problems (P = .008) than those undergoing PO-VMAT at 12 months. There was no significant between-group difference in any individual items at 24 months, however. CONCLUSIONS Bowel and urinary HRQOL is largely similar for patients receiving PO-VMAT and WP-VMAT during 24 months of follow-up, with the only differences seen in responses to specific bowel HRQOL items at 12 months.

Novel Anisotropic Margin Calculation Based On the Cumulative Frequency Distribution of Uncertainties in the Clinical Target Volume

Objective: The purpose of this study was to determine the PTV margins from the cumulative frequency of uncertainties of the clinical target volume (CTV) position obtained using hybrid-image guided radiotherapy (H-IGRT) with volumetric-modulated arc therapy (VMAT). Materials and Methods: Study participants were 22 patients with intermediate-risk prostate cancer who underwent VMAT. All patients were treated using the following image-guided (IG) procedure: 1) no-correction skin mark setup (no- IG); 2) bony anatomy registration with 2D-imaging (2D-IG); and 3) organ registration using CBCT images (3D-IG). The systematic (Σtot) and random (σtot) errors were obtained from the no-IG, 2D-IG, and 3D-IG registration images of 198 fractions. The PTV margin was computed using the cumulative frequency distribution of the actual position errors of the CTV, and which was compared with the formulation by MPTV = 2.5 Σtot + 0.7 σtot. Results: The margin size of 3D IG procedure was as follows: 3D-IG: 7.6, 5.4, and 3.5 mm for the AP, SI, and LR axes, respectively. Using MPTV = 2.5 Σtot + 0.7 σtot: 3D-IG: 4.2, 3.7, and 1.3 mm for the AP, SI, and LR axes, respectively. In MPTV: = α Σtot + β σtot, the coefficients α and β were α = 3.4, 2.3, and 4.6 and β = 2.9, 3.0, and 3.0 for AP, SI, and LR, respectively. Conclusion: The margin size (MPTV) calculated by our modified formulation based on the margin direction satisfied 99% of the prescription dose coverage in each direction and a minimum of 95% of the dose coverage to the CTV for all patients using H-IGRT